Assessing average slip rates of strike-slip faults in Japanese mountains based on geomorphic analyses of lidar DEMs

For the active strike-slip faults with no chronological information such as those in mountainous and arid regions, it is desired to quantitatively assess their slip rates from geomorphic properties such as channel offset. We analyzed the relationships between channel offset and other geomorphic properties to evaluate the geomorphic response to active strike-slip faulting in Japanese mountains. Using high resolution lidar DEMs (0.5 m - 2 m), seven active strike-slip faults (Shikano F., Umehara F., Daguchi F., Takayama F., Neodani F., Atera F., and Atotugawa F.) with various slip rates ranging from ~0.01 mm/yr to ~10 mm/yr were examined. Channel offsets were automatically identified and extracted. Analyses of channel offsets revealed positive linear relationships (with slope α) between offset amounts and stream length, watershed area or watershed volume, due to accumulation of offset with watershed evolution. Further, the slope α shows positive correlations with average slip rate, and thus may be used as criteria to quantitatively evaluate the slip rates of strike-slip faults. Our analyses also revealed that hillslope angle affects α value, suggesting the influence of erosion rate on α value. We therefore measured the watershed erosion rate using in situ cosmogenic nuclide method to strictly constrain the relationship between α value, average slip rate, and erosion rate. Our study may provide a new approach for quantitatively assessing average slip rates of the strike-slip faults.